Options

Options are defined with the .option() method, also serving as documentation for the options. Each option can have a short flag (single character) and a long name, separated by a comma or space or vertical bar ('|').

The options can be accessed as properties on the Command object. Multi-word options such as "--template-engine" are camel-cased, becoming program.templateEngine etc. See also optional new behaviour to avoid name clashes.

Multiple short flags may optionally be combined in a single argument following the dash: boolean flags, the last flag may take a value, and the value. For example -a -b -p 80 may be written as -ab -p80 or even -abp80.

You can use -- to indicate the end of the options, and any remaining arguments will be used without being interpreted. This is particularly useful for passing options through to another command, like: do -- git --version.

Options on the command line are not positional, and can be specified before or after other command arguments.

Common option types, boolean and value

The two most used option types are a boolean flag, and an option which takes a value (declared using angle brackets). Both are undefined unless specified on command line.

Other option types, negatable boolean and flag|value

You can specify a boolean option long name with a leading no- to set the option value to false when used. Defined alone this also makes the option true by default.

If you define --foo first, adding --no-foo does not change the default value from what it would otherwise be. You can specify a default boolean value for a boolean flag and it can be overridden on command line.

Custom option processing

You may specify a function to do custom processing of option values. The callback function receives two parameters, the user specified value and the previous value for the option. It returns the new value for the option.

This allows you to coerce the option value to the desired type, or accumulate values, or do entirely custom processing.

You can optionally specify the default/starting value for the option after the function.

Required option

You may specify a required (mandatory) option using .requiredOption. The option must have a value after parsing, usually specified on the command line, or perhaps from a default value (say from environment). The method is otherwise the same as .option in format, taking flags and description, and optional default value or custom processing.

Version option

The optional version method adds handling for displaying the command version. The default option flags are -V and --version, and when present the command prints the version number and exits.

program.version('0.0.1');

$ ./examples/pizza -V
0.0.1

You may change the flags and description by passing additional parameters to the version method, using the same syntax for flags as the option method. The version flags can be named anything, but a long name is required.

program.version('0.0.1', '-v, --vers', 'output the current version');

Commands

You can specify (sub)commands using .command() or .addCommand(). There are two ways these can be implemented: using an action handler attached to the command, or as a stand-alone executable file (described in more detail later). The subcommands may be nested (example).

In the first parameter to .command() you specify the command name and any command arguments. The arguments may be <required> or [optional], and the last argument may also be variadic....

You can use .addCommand() to add an already configured subcommand to the program.

For example:

// Command implemented using action handler (description is supplied separately to `.command`)
// Returns new command for configuring.
program
.command('clone <source> [destination]')
.description('clone a repository into a newly created directory')
.action((source, destination) => {
console.log('clone command called');
});
// Command implemented using stand-alone executable file (description is second parameter to `.command`)
// Returns `this` for adding more commands.
program
.command('start <service>', 'start named service')
.command('stop [service]', 'stop named service, or all if no name supplied');
// Command prepared separately.
// Returns `this` for adding more commands.
program
.addCommand(build.makeBuildCommand());

Configuration options can be passed with the call to .command() and .addCommand(). Specifying true for opts.hidden will remove the command from the generated help output. Specifying true for opts.isDefault will run the subcommand if no other subcommand is specified (example).

Specify the argument syntax

You use .arguments to specify the arguments for the top-level command, and for subcommands they are usually included in the .command call. Angled brackets (e.g. <required>) indicate required input. Square brackets (e.g. [optional]) indicate optional input.

Action handler (sub)commands

You can add options to a command that uses an action handler. The action handler gets passed a parameter for each argument you declared, and one additional argument which is the command object itself. This command argument has the values for the command-specific options added as properties.

A command's options on the command line are validated when the command is used. Any unknown options will be reported as an error.

Stand-alone executable (sub)commands

When .command() is invoked with a description argument, this tells Commander that you're going to use stand-alone executables for subcommands. Commander will search the executables in the directory of the entry script (like ./examples/pm) with the name program-subcommand, like pm-install, pm-search. You can specify a custom name with the executableFile configuration option.

You handle the options for an executable (sub)command in the executable, and don't declare them at the top-level.

A help command is added by default if your command has subcommands. It can be used alone, or with a subcommand name to show further help for the subcommand. These are effectively the same if the shell program has implicit help:

shell help
shell --help
shell help spawn
shell spawn --help

Custom help

You can display extra information by listening for "--help". (example)

Avoiding option name clashes

The original and default behaviour is that the option values are stored as properties on the program, and the action handler is passed a command object with the options values stored as properties. This is very convenient to code, but the downside is possible clashes with existing properties of Command.

There are two new routines to change the behaviour, and the default behaviour may change in the future:

storeOptionsAsProperties: whether to store option values as properties on command object, or store separately (specify false) and access using .opts()

passCommandToAction: whether to pass command to action handler, or just the options (specify false)

createCommand()

createCommand is also a method of the Command object, and creates a new command rather than a subcommand. This gets used internally when creating subcommands using .command(), and you may override it to customise the new subcommand (examples using subclass and function).

Node options such as --harmony

You can enable --harmony option in two ways:

Use #! /usr/bin/env node --harmony in the subcommands scripts. (Note Windows does not support this pattern.)

Use the --harmony option when call the command, like node --harmony examples/pm publish. The --harmony option will be preserved when spawning subcommand process.

Debugging stand-alone executable subcommands

An executable subcommand is launched as a separate child process.

If you are using the node inspector for debugging executable subcommands using node --inspect et al, the inspector port is incremented by 1 for the spawned subcommand.

If you are using VSCode to debug executable subcommands you need to set the "autoAttachChildProcesses": true flag in your launch.json configuration.

Override exit handling

By default Commander calls process.exit when it detects errors, or after displaying the help or version. You can override this behaviour and optionally supply a callback. The default override throws a CommanderError.

The override callback is passed a CommanderError with properties exitCode number, code string, and message. The default override behaviour is to throw the error, except for async handling of executable subcommand completion which carries on. The normal display of error messages or version or help is not affected by the override which is called after the display.

License

Support

Commander 5.x is fully supported on Long Term Support versions of Node, and is likely to work with Node 6 but not tested. (For versions of Node below Node 6, use Commander 3.x or 2.x.)

The main forum for free and community support is the project Issues on GitHub.

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